1. Field of the Invention
The present invention relates to a pattern forming system wherein a pattern formed on a reticule is demagnified and projected on a surface of a wafer by a step- and repeat photolithographic system with demagnification (hereinafter called stepper) and an application of such a system to an apparatus for exposing photoresist formed on the wafer in a step and repeat system.
2. Description of the Related Art
Conventionally, in a case where a pattern formed on a reticule is demagnified and projected on the surface of a wafer, and the pattern is formed on the surface of the wafer, the pattern formed on the reticule is formed on the surface of the wafer by one shot. Generally, a plurality of shots can be carried out to one wafer, and a plurality of the same patterns are formed on the surface of the wafer in a matrix manner. As a method for forming the plurality of the same patterns on the entire surface of the wafer by the plurality of shots, the following four cases can be considered as shown in Table 1.
TABLE 1 ______________________________________ Array Method ______________________________________ X Direction Even Even Odd Odd Number Number Number Number Y Direction Even Odd Even Odd Number Number Number Number FIG. 7 FIG. 8 FIG. 9 FIG. 10 ______________________________________
The above four cases can be considered based on the assumption of a two-dimensional coordinate on the surface of the wafer. As shown in FIG. 1, the first case relates to shot regions (1 to 38), and shows that an even number of shot regions in which the patterns formed on the reticule exist in the respective X and Y directions from an origin of the coordinate axes. As shown in FIG. 2, the second case relates to shot regions 1 to 40 and shows that an even number of shot regions exist in the X direction and that an odd number of shot regions exist in the Y direction. As shown in FIG. 3, the third case relates to shot regions 1 to 39, and shows that an odd number of shot regions exist in the X direction and that an even number of shot regions exist in the Y direction. As shown in FIG. 4, the fourth case relates to shot regions (1 to 37), and shows that an odd number of shot regions exist in the respective X and Y directions.
In the mentioned cases, assuming that, for example, a diameter of the wafer is 5 inches and a size of one shot region is 15 mm.times.15 mm, the number of complete patterns to be formed in the wafer will be 38 according to the first case of FIG. 1, 40 according to the second case of FIG. 2, 39 according to the third case of FIG. 3, and 37 according to the fourth case of FIG. 4. Therefore, if the patterns to be formed by one shot constitutes one integrated circuit (IC), the maximum number of ICs to be obtained from one wafer can be obtained in the array method of the shot regions shown in FIG. 2. In other words, if the patterns on the reticule are formed on the surface of the wafer by use of the array method of the shot regions shown in FIG. 2, the maximum number of ICs can be obtained from one wafer, and efficiency of IC production can be improved.
In a case where the patterns formed on the reticule are actually formed on the surface of the wafer, it is necessary to chose the case in which the maximum number of ICs can be obtained from one wafer. In this case, conventionally, workers must actually count the number of ICs to be obtained from one wafer in each case in order to select the case in which the maximum number of ICs can be obtained.
However, if the size of each IC is made small, and the number of ICs to be obtained from one wafer is increased, counting the number of ICs is extremely hard work for the workers.
FIG. 5 shows the relationship between the size of the chip and the gross of the chip gross relating to an experimental value and a theoretical value. A theoretical value shown by a broken line of FIG. 5 is a number, which is obtained by dividing an area of a main surface of the wafer by an area of one IC. A chip gross shown by a solid line of FIG. 5 is a number of ICs, which are actually formed on the main surface of the wafer in a complete shape if the patterns are formed on the surface of the wafer by a predetermined array method. In other words, if the size of the IC is 3 mm.times.3 mm, both the experimental value of the chip gross and the theoretical value are about 1300, respectively. Due to this, it is impossible for workers to count the number of ICs formed on the surface of the wafer one by one.